ppnP (PP_4248) encodes a broad-specificity pyrimidine/purine nucleoside phosphorylase (EC 2.4.2.1, EC 2.4.2.2) of the cupin-fold PpnP family. It catalyzes reversible phosphorolysis of diverse purine and pyrimidine nucleosides (uridine, adenosine, guanosine, cytidine, thymidine, inosine, xanthosine), yielding the free nucleobase plus alpha-D-ribose 1-phosphate, and functions in cytoplasmic nucleoside salvage/catabolism. The KT2440 enzyme itself has not been biochemically characterized; the functional assignment rests on HAMAP-Rule MF_01537 and falcon family/ortholog evidence rather than direct experimental proof.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004731 purine-nucleoside phosphorylase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Purine-nucleoside phosphorylase activity is one of PpnP's supported substrate activities. Reason: UniProt describes phosphorolysis of purine ribonucleosides including adenosine, guanosine, inosine, and xanthosine. Falcon family/ortholog evidence independently describes PpnP as a broad-specificity enzyme acting on purine nucleosides. Supporting Evidence: file:PSEPK/ppnP/ppnP-uniprot.txt a purine D-ribonucleoside + phosphate file:PSEPK/ppnP/ppnP-goa.tsv GO:0004731 purine-nucleoside phosphorylase activity file:PSEPK/ppnP/ppnP-deep-research-falcon.md is explicitly described as a broad-specificity pyrimidine/purine nucleoside phosphorylase in bacterial purine salvage context |
| GO:0004850 uridine phosphorylase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Uridine phosphorylase activity is directly supported by the UniProt/Rhea reaction list. Reason: PpnP can use uridine as substrate; this is one of the broad pyrimidine activities of the enzyme. Supporting Evidence: file:PSEPK/ppnP/ppnP-uniprot.txt uridine + phosphate = alpha-D-ribose 1-phosphate + uracil file:PSEPK/ppnP/ppnP-goa.tsv GO:0004850 uridine phosphorylase activity file:PSEPK/ppnP/ppnP-deep-research-falcon.md PpnP is explicitly reported to act on multiple nucleosides, including |
| GO:0005829 cytosol | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: Cytosol is plausible context but not the core function. Reason: PpnP is reviewed as a soluble nucleoside phosphorylase; localization is inferred (TreeGrafter IEA) and falcon likewise infers cytoplasmic localization from salvage pathway architecture, so it should remain non-core. Supporting Evidence: file:PSEPK/ppnP/ppnP-goa.tsv GO:0005829 cytosol file:PSEPK/ppnP/ppnP-deep-research-falcon.md because nucleosides are first imported by membrane transporters and PpnP products feed intracellular regulation/metabolism |
| GO:0009032 thymidine phosphorylase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Thymidine phosphorylase activity is directly supported by the UniProt/Rhea reaction list. Reason: PpnP can use thymidine as substrate; deoxynucleoside phosphorolysis is part of the broad PpnP activity. Supporting Evidence: file:PSEPK/ppnP/ppnP-uniprot.txt thymidine + phosphate = 2-deoxy-alpha-D-ribose 1-phosphate file:PSEPK/ppnP/ppnP-goa.tsv GO:0009032 thymidine phosphorylase activity |
| GO:0016154 pyrimidine-nucleoside phosphorylase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Pyrimidine-nucleoside phosphorylase activity is supported by PpnP's broad pyrimidine substrate range. Reason: UniProt lists cytidine, thymidine, and uridine phosphorolysis (EC 2.4.2.2). Falcon independently describes PpnP as a broad-specificity pyrimidine/purine nucleoside phosphorylase. This is one of the two core enzymatic activities. Supporting Evidence: file:PSEPK/ppnP/ppnP-uniprot.txt Can use uridine, file:PSEPK/ppnP/ppnP-goa.tsv GO:0016154 pyrimidine-nucleoside phosphorylase activity file:PSEPK/ppnP/ppnP-deep-research-falcon.md that cleaves nucleosides with phosphate to yield a nucleobase and D-ribose-1-phosphate |
| GO:0047975 guanosine phosphorylase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Guanosine phosphorylase activity is directly supported by the UniProt/Rhea reaction list. Reason: PpnP can use guanosine as substrate. Falcon notes that in metabolic-engineering studies ppnP is treated as one of the guanosine phosphorylases in guanosine degradation, consistent with this activity. Supporting Evidence: file:PSEPK/ppnP/ppnP-uniprot.txt guanosine + phosphate = alpha-D-ribose 1-phosphate + guanine file:PSEPK/ppnP/ppnP-goa.tsv GO:0047975 guanosine phosphorylase activity file:PSEPK/ppnP/ppnP-deep-research-falcon.md its deletion measurably increases nucleoside product titres in industrially relevant fermentation contexts |
| GO:0009164 nucleoside catabolic process | IEA GO_REF:0000120 | NEW | Summary: PpnP should be connected to nucleoside catabolism because it phosphorolyzes diverse purine and pyrimidine nucleosides. Reason: The fetched GOA table has multiple substrate-specific nucleoside phosphorylase molecular-function rows but no biological-process annotation. GO:0009164 captures the catabolic process implied by broad nucleoside phosphorolysis. Falcon confirms a catabolic role downstream of nucleoside uptake (producing bases plus ribose-1-phosphate) and notes that ppnP deletion increases nucleoside titres in fermentation, evidencing its role as a catabolic sink. UniProt also notes reverse reactions, but the phosphorolytic/catabolic direction is the principal process represented here; GO:0009116 nucleoside metabolic process would be broader and less informative. Supporting Evidence: file:PSEPK/ppnP/ppnP-uniprot.txt Catalyzes the phosphorolysis of diverse nucleosides file:PSEPK/ppnP/ppnP-uniprot.txt D-ribose 1-phosphate and the respective free bases file:PSEPK/ppnP/ppnP-deep-research-falcon.md downstream of nucleoside uptake, producing bases and ribose-1-phosphate for reuse |
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Download this section (compressed HTML)Q: Which nucleosides dominate PpnP flux in KT2440 under nutrient scavenging or stationary-phase conditions?
Experiment: Measure purified PpnP kinetics across purine and pyrimidine nucleosides and profile nucleoside utilization in a ppnP knockout.
Type: enzyme substrate panel and growth/metabolite assay
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